A liquid crystal display device has been widely utilized for a watch, an electronic calculator as well as a word processor, a television set, etc. Of these liquid crystal display device, particularly frequently used is a TN type (twisted nematic type) liquid crystal display device which utilizes optical anisotropy and dielectric anisotropy of a liquid crystal material.
At present, as characteristics required for a liquid crystal material to be used for liquid crystal display devices, there may be mentioned that a crystal-nematic point (C-N point) is low and a nematic-isotropic liquid point (N-I point) is high in order to have a wide liquid crystal temperature range, a viscosity is low in order to obtain a rapid electro-optical response rate, an optical anisotropy (.DELTA.n) is coincide with the constitution of a panel in order to have a wide visual scope, a dielectric anisotropy (.DELTA..epsilon.) is large to lower a driving voltage, and it is chemically and optically stable.
Until now, any single liquid crystal compound satisfying all the characteristics as mentioned above has not yet been found. Thus, it is the present status that several kinds of liquid crystal compounds having various characteristics are mixed or further various kinds of non-liquid crystal compounds are mixed for practical use.
Also, depending on the liquid crystal display device, degree of the above characteristics to be required is different so that development of a novel liquid crystal compound providing characteristics suitable for the objects of a liquid crystal display device is required.
Heretofore, as a benzyl ether series compound to be used as a liquid crystal composition, there have been known trans-4-(trans-4-alkylcyclohexyl)cyclohexyl-4-substituted benzyl ether substituted by CN, F, Cl or Br (Japanese Patent Publication No. 50734/1991) or trans-4-(trans-4-alkenylcyclohexyl)cyclohexyl-3,4-di-substituted benzyl ether substituted by F or Cl (Japanese Laid-Open Patent Application No. 157925/1989), and further trans-4-alkylcyclohexyl-4-substituted benzyl ether (Japanese Patent Publication No. 14088/1992).
However, other benzyl ether compound than the above such as, for example, a compound wherein a straight alkylcyclohexyl group or a straight alkylbicyclohexyl group is bonded to a difluorobenzyl ether has never been known.
As described above, a compound which satisfy all the characteristics required for a liquid crystal material has not been found at the present stage, and even when various liquid crystal compounds or non-liquid crystal compounds are used in combination, there is no material which satisfies the above characteristics sufficiently. In addition, each of these compounds has merits and demerits in their characteristics. Therefore, as mentioned above, it is present status that various liquid crystal and non-liquid crystal compounds are used in combination for practical use, and thus, more excellent novel liquid crystal compounds are required to be provided.